It is known that spiral accumulators are temporary storage devices incorporated in a processing or transformation line, such as a shaping line, enabling a tube to be obtained from a length of metal strip. The accumulator contains a number of spiral-wound turns of the strip. These turns form a reserve which, particularly when a supply spool is exhausted, permits a new spool to be butt-joined while the line continues to be supplied by the reserve in the accumulator.
In known machines of this type the turns of strip are supported by a horizontal plate. Accordingly, to supply the line downstream, the inside turn must be caused to pass above the spiral-wound turns. This deflecting device must thus be mounted inside the spiral to guide the inside turn, and must prevent differences in tension from being created between its lower and upper edges. Such differences of tension would cause the lengths of the two edges to be different such that the edge stretched the most would crinkle. The latter is unacceptable if, for example, it is desired to weld the strip edge to edge to form a tube.
A spiral accumulator including a positively rotatable annular plate with a vertical axis is known. An inner crown and outer crown of rollers loosely mounted with respect to fixed vertical axes are disposed respectively at the inside periphery and the outside periphery of the plate to contain the turns of the strip. The deflecting device is composed of a central drum disposed inside the inner circle of rollers and freely rotatably mounted with respect to an axis tilted relative to the vertical axis of the plate.
This deflecting device, due to the inclination of its axis with respect to the vertical, guides the inside turn to some extent, making it pass above the other turns. But it will be seen that during this deflection the inside turn of the strip would not of itself assume a shape such that it can be applied to a cylinder. Thus, a cylindrical deflecting device, even with a tilted axis, is not the ideal guide for preventing differential lengthening of the strip.